This invention relates to the treatment of hydrocarbon-containing formations. More particularly, the invention relates to fluids which are used to optimize the production of hydrocarbon from a formation, known as well completion fluids, and to methods of treating such formations. The invention specifically relates to scale inhibition treatment compositions and methods.
Contact of various inorganic compounds present in hydrocarbon bearing rock formations with compounds present in oilfield process fluids, such as seawater, sometimes leads to the formation and precipitation of “scale”, that is, water insoluble salts, such as barium sulfate and calcium carbonate, that can clog formation porosity and inhibit the flow of hydrocarbons from the formation to the wellbore. Scale inhibitors are used in oil fields to control or prevent scale deposition in the production conduit or completion system. Scale-inhibitor chemicals may be continuously injected through a downhole injection point in the completion, or periodic squeeze treatments may be undertaken to place the inhibitor in the reservoir matrix for subsequent commingling with produced fluids. Some scale-inhibitor systems integrate scale inhibitors and fracture treatments into one step, which guarantees that the entire well is treated with scale inhibitor. In this type of treatment, a high-efficiency scale inhibitor is pumped into the matrix surrounding the fracture face during leakoff. It adsorbs to the matrix during pumping until the fracture begins to produce water. As water passes through the inhibitor-adsorbed zone, it dissolves sufficient inhibitor to prevent scale deposition. The inhibitor is better placed than in a conventional scale-inhibitor squeeze, which reduces the retreatment cost and improves production.
Scale inhibitor squeeze fluids are typically Newtonian fluids which have difficulties to reach low permeability regions of hydrocarbon formations, especially horizontal hydrocarbon well formations. As a result, squeeze treatment with such fluids is not efficient in these regions and may cause the deposit of scale which can then block these regions, resulting in decreased production rates.
SPE paper 94593 describes using fully viscosified scale squeeze fluids to help optimize the squeeze treatment by allowing the fluid to reach the low permeability region and the horizontal zones. This SPE paper describes use of a xanthan polymer to place scale inhibitor in horizontal well N19z. However, the paper admits that the xanthan needed a breaker to recover all of it. Leaving such compounds in the well could then be damaging for the formation which will eventually decrease the production efficiency.
U.S. Pat. No. 6,903,054, Fu, et al., assigned to Schlumberger, Inc., which is hereby incorporated by reference in its entirety, describes a method for treating hydrocarbon-containing formations with a well treating fluid which includes a self-diverting acid that includes about 1-30% by weight of at least one acid selected from the group consisting of hydrochloric, sulfuric, phosphoric, formic, acetic, citric, maleic, and hydrofluoric acids, 1 to 20% by volume of a viscoelastic surfactant, and 0.7 to 20% by weight scale inhibitor.
It would be of great commercial value and importance to provide a hydrocarbon formation treatment scale inhibition composition and method of using that composition in a squeeze treatment which did not require a breaker to remove the composition and caused reduced formation damage, or did not damage the formation at all.